Hard refractory materials are known and are used extensively in such applications as mining tool bits, metal cutting, milling, and boring tools, metal drawing dies, wear-resistant machine parts and the like. It is also known that the service properties such as wear, high temperature and chemical resistance of such materials may be enhanced by the application of one or more thin coatings of, for example, metal carbides, metal nitrides, or ceramics to the hard refractory substrate.
"Hard refractory," as used herein, refers to fully dense, wear resistant materials not melting or dissociating below 1000.degree. C., for example ceramic compositions based on Al.sub.2 O.sub.3, Si.sub.3 N.sub.4, SiC, silicon aluminum oxynitride, and related materials; cemented metal carbides such as WC-Co; and metal carbides, nitrides, and carbonitrides, such as TiC and TiN. Such materials may have a monolithic or composite microstructure.
Great strides have been made in improved performance of these coated substrates, for example in machining applications, by refinement of the substrate compositions and by applying simple layers or various combinations of superimposed layers of coating materials. However, increasingly stringent use conditions, for example use at high cutting speeds or in extremely high temperatures and/or corrosive environments, are placing increasing demands upon the performance of such materials.
The invention described herein and recited in the appended claims provides a process for depositing a wear resistant composite coating of controlled composition and distribution on a hard refractory substrate to produce an article showing improved abrasion resistance under extreme conditions of use.